Encapsulating functional guest molecules into the cavities of crystalline porous materials makes it possible to engineer these materials for drug delivery (Horcajada, et al., Nat. Mater. 2010, 9, 172; Rimoli, et al., J. Biomed. Mater. Res. A 2008, 87A, 156), sensing (Yanai, et al., Nat. Mater. 2011, 10, 787; McGilvray, et al., Chem. Commun. 2006, 4401), electrical conductivity (Talin, et al., Science 2014, 343, 66; Cardin, D. J., Adv. Mater. 2002, 14, 553), luminescence (Muller, et al., Photochem. Photobiol. Sci. 2010, 9, 846; Calzaferri, et al., Angew. Chem. Int. Ed. 2003, 42, 3732; Martinez-Martinez, et al., J. Phys. Chem. C 2012, 116, 26084), and energy conversion (Wang, et al., ACS Catalysis 2012, 2, 2630; Son, et al., J. Am. Chem. Soc. 2013, 135, 862; Dutta, et al., J. Phys. Chem. Lett. 2011, 2, 467). Host-guest crystalline porous materials have been studied in aluminosilicate zeolites since the 1980s (Corma, et al., Eur. J. Inorg. Chem. 2004, 2004, 1143).
Approaches for encapsulating large and more diverse guests are still limited to a few specific metal-organic framework (MOF) types. For example, negatively charged MOFs have been utilized to incorporate cationic organic compounds and metals (Li, et al., J. Am. Chem. Soc. 2014, 136, 1202; Alkordi, et al., J. Am. Chem. Soc. 2008, 130, 12639; Larsen, J. Mater. Chem. A 2013, 1, 14133), and MOFs with unoccupied sites can encapsulate guests through dative bonds (Talin, et al., Science 2014, 343, 66). Many MOFs lack framework charge or unoccupied sites, which prohibits the general applicability of these methods. Alternatively, guest molecules have been covalently bound to the bridging ligands of the frameworks (Costa, et al., J. Eur. J. Inorg. Chem. 2008, 1551), but the loss of degrees of freedom for tethered homogeneous catalysts could lead to decreased activity or selectivity in catalytic applications (Lee, et al., Chem. Soc. Rev. 2009, 38, 1450).
Encapsulation of guest molecules in MOFs by diffusion is generally limited to guests that are smaller than the MOF aperture size (Alkordi, et al., J. Am. Chem. Soc. 2008, 130, 12639). This limitation commonly leads to guest molecule leaching, which is particularly problematic for catalytic applications.
There is thus a need in the art for a novel method of encapsulating a guest molecule having a diameter larger than the aperture size of the host, such as a MOF. The present invention fulfills this need.